3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
The 3GPP LTE-A employs various techniques such as carrier aggregation, relay, etc. The 3GPP LTE system is a single carrier system supporting only one bandwidth (i.e., one component carrier) among {1.4, 3, 5, 10, 15, 20}MHz. On the other hand, the LTE-A employs multiple carriers using carrier aggregation. The carrier is defined with a center frequency and a bandwidth. A multiple-carrier system uses a plurality of component carriers having a narrower bandwidth than a full bandwidth.
A user equipment (UE) persistently performs measurement to maintain quality of a radio link with a serving cell from which the UE receives a service. The UE determines whether communication is impossible in a current situation due to deterioration of the quality of the radio link with the serving cell. If it is determined that the quality of the serving cell is so bad that communication is currently impossible, the UE determines the current situation as a radio link failure.
A single carrier system uses only one carrier, and thus the radio link failure is declared when quality of one carrier is persistently bad.
A multiple carrier system uses a plurality of component carriers, and thus even if any one component carrier has bad quality, other component carriers may have good quality. This is because a channel state of component carriers having different frequency bands has a low correlation.
Accordingly, there is a need for a method capable of determining and processing a failure of a component carrier in a multiple carrier system.